Jun 262012
 

I have had a lot of battles with the pro-corsi crowd with regards to the merits of using Corsi as a player evaluation tool.  I still get people dismissing my goal based analysis (which seems really strange since goals are what matters in hockey) so I figured I should summarize my position in one easy to understand post.  So, with that, here are 10 significant reasons why I don’t like to use a corsi based player analysis.

1.  Look at the list of players with the top on-ice shooting percentage over the past 5 seasons and compare it to the list of players with the top corsi for per 20 minutes of ice time and you’ll find that the shooting percentage list is far more representative of top offensive players than the top corsi for list.

2.  Shooting percentage is a talent and is sustainable and three year shooting percentage is as good a predictor of the following 2 seasons goal scoring rates as 3 year fenwick rates and 3 year goal rates are a far better predictor.

r^2
2007-10 FF20 vs 2010-12 GF20 0.253
2007-10 SH% vs 2010-12 GF20 0.244
2007-10 GF20 vs 2010-12 GF20 0.363

3.  I have even shown that one year GF20 is on average as good a predictor of  the following seasons GF20 as FF20 is as a predictor of the following seasons FF20 so with even just one full season of data goal rates are as good a metric of offensive talent as fenwick rate is.  Only when the sample size is less than one season (and for almost all NHL regulars we have at least a seasons worth of data) is fenwick rate a better metric for evaluating offensive talent.

4.  Although difficult to identify, I believe I have shown players can suppress opposition shooting percentage.

5.  Zone starts affect shots/corsi/fenwick stats significantly more than they affect goal stats thus the non-adjusted shot/corsi/fenwick data are less useful than the non-adjusted goal data.

6.  Although not specifically a beef with Corsi, much of the corsi analysis currently being done does not split out offensive corsi and defensive corsi but rather looks at them as a percentage or as a +/- differential.  I believe this is a poor way of doing analysis because it really is useful to know whether a player is good because he produces a lot of offense or whether the player is good because he is great defensively.  Plus, when evaluating a player offensively we need to consider the offensive capability of his team mates and the defensive capability of his opposition, not the overall ability of those players.

7.  I have a really hard time believing that 8 of the top 9 corsi % players over the past 5 seasons are Red Wing players because they are all really talented and had nothing to do with the system they play or some other non-individual talent factor.

8.  Try doing a Malkin vs Gomez fenwick/corsi comparison and now do the same with goals.  Gomez actually has a very good and very comparable fenwick rating to Malkin, but Malkin is a far better player at producing goals thanks to his far superior on-ice shooting percentage (FSh% = fenwick shooting percentage = goals / fenwick for).  Gomez every single season has a much poorer on-ice shooting percentage than Malkin and this is why Malkin is the far better player.  Fenwick/Corsi doesn’t account for this.

Malkin Gomez Malkin Gomez Malkin Gomez
Season(s) FF20 FF20 GF20 GF20 FSh% FSh%
2011-12 16.5 14.0 1.301 0.660 7.9% 4.7%
2010-11 16.1 16.4 0.949 0.534 5.9% 3.3%
2009-10 15.3 14.2 1.112 0.837 7.3% 5.9%
2008-09 12.4 16.8 1.163 0.757 9.4% 4.5%
2007-08 14.1 15.9 1.206 0.792 8.5% 5.0%
2007-11 14.7 14.7 1.171 0.745 8.0% 5.1%

 

So there you have it.  Those are some of the main reasons why I don’t use corsi in player analysis.  This isn’t to say Corsi isn’t a useful metric.  It is a useful metric in identifying which players are better at controlling play. Unfortunately, controlling play is only part of the game so if you want to conduct a complete thorough evaluation of a player, goal based stats are required.

 

  5 Responses to “Eight Reasons I Don’t Like Fenwick/Corsi in Player Analysis”

  1.  

    Can’t get a goal without a shot.

  2.  

    I like corsi/fenwick a lot with regard groups, coaches and systems evaluation.

  3.  

    Thats why most people I know there use corsi, also uses zone starts, quality of time and quality of competition, corsi on/off, G/60 and A1/60 to paint a picture of the players qualities.

    •  

      I think you missed the point a little. Corsi is an incomplete evaluation so corsi on/off and quality of competition metrics based on corsi (which is what pro-corsi people use) are incomplete metrics as well. Zone starts are important and I consider them (or usually factor them out with zone start adjustments). I see some, but generally not a lot of use of G/60 or A1/60 in most corsi based player evaluations.

      •  

        One thing I have learned about Corsi is that you cannot use it directly to compare two players from different teams, but its a great tool to evaluate players on a team or compare how if they are used as a first pair against tough competition or not.

        I know you say players can shot suppress, but should Flyers players be punished for poor goaltending in terms of GA when they ranked very low in shots against?

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